As a kind of flat panel display device, Thin Film Transistor Liquid Crystal Display (TFT-LCD) is increasingly used by people due to its advantages such as small size, low power consumption, no radiation, relatively low production cost and the like.
The TFT-LCD comprises an array substrate and a color filter substrate. A liquid crystal layer is provided between the array substrate and the color filter substrate, and an electric field is generated in the liquid crystal layer by respectively applying voltages on a pixel electrode provided on the array substrate and on a common electrode provided on the color filter substrate or the array substrate. Then, a transmittance of light passing through the liquid crystal layer is adjusted by adjusting the magnitude of the electric field, so that expected images are displayed.
In the case that the above common electrode and pixel electrode are both provided on the array substrate, the common electrode and the pixel electrode may be according to different layers; and the electrode in the upper layer is an electrode comprising slits and the electrode in the lower layer is a plate-shaped electrode (or an electrode comprising slits). The display device constructed by using the above array substrate is a display device of Advanced-Super Dimensional Switching (AD-SDS, and ADS in short) type. For example, as shown in FIG. 1, the common electrode 10a is the plate-shaped electrode, the pixel electrode 11a is the electrode comprising slits, and the pixel electrode 11a is provided above the common electrode 10a. In the above display device of ADS type, a multi-dimensional electric field is formed with both an electric field generated at edges of slits (the slits of the pixel electrode 11a) in a same plane and an electric field generated between the electrode comprising slits (the pixel electrode 11a) and a plate-like electrode (the common electrode 10a), so that liquid crystal molecules at all orientations, which are located directly above the electrodes or between the slits in the liquid crystal layer, can be rotated. In this way, the work efficiency of liquid crystal can be enhanced and the light transmittance can be increased. The display device of ADS type has advantages of high image quality, high resolution, high transmittance, low power consumption, wide viewing angle, and the like.
In order that a common voltage is input to the common electrode 10a of each sub-pixel 1a, a common electrode line 101a parallel to a gate line 100a is generally provided on at least one side of the gate line 100a and is connected to the common electrodes 10a of the sub-pixels 1a in a same row. The common voltage is supplied to the common electrode 10a by the above common electrode line 101a. 
However, a portion of a display region of the above sub-pixel 1a is occupied by the common electrode line 101a, thus the aperture ratio of the display device is reduced and the display effect of the display device is reduced.